1. Beat cream cheese, sour cream and mayonnaise until smooth.
2. Spread on a 12-14 pizza pan.
3. Refrigerate 1 hour.
4. Brown beef over meadium heat; drain.
5. Add taco seasoning and tomato sauce; cook and stir 5 minutes.
6. Cool completely.
7. Spread over cream cheese layer.
8. Refrigerate.
9. Just before serving, sprinkle with lettuce, onion, tomato and cheese.
10. Serve with chips.